17 isoflavones, but significantly decreased the content of the malonylglucoside forms
malonyldaidzin, malonylglycitin, and malonylgenistin Xu and Chang 2008. Therefore, this research indicated that isoflavones from phenolic group obtained
from 80 acetone extract were the responsible components affecting the changes of antioxidant capacity of tempe during heating.
On the other hand, the decline of antioxidant compounds in tempe was due to the increase of water soluble antioxidant subtances to 2 of salt solution.
Thermal process might decrease firmness and adhesion of cell walls Van Buren 1979, thus it induced releasing bound phenolic compounds, such as flavonoids,
accumulated in the vacuoles Brecht et al. 2008. Briefly, as longer heating time and higher temperature, the bound antioxidant components were more liberated
from cell and leached into salt solution.
Figure 7 Effects of heating on DPPH scavenging capacity of tempe at 75, 85, and 95
o
C.
0,00 1,00
2,00 3,00
4,00
30 60
90 120
DP P
H sca
v en
g in
g ca
p a
ci ty
m M
AA Eg
Time min
Tempe
75ºC 85ºC
95ºC 0,00
1,00 2,00
3,00 4,00
30 60
90 120
DPPH sc a
v en
g in
g c
a p
a city
m M
o f
AA Eg
Time min
Salt Solution
75ºC 85ºC
95ºC
0,00 1,00
2,00 3,00
4,00
30 60
90 120
DPPH sc a
v en
g in
g c
a p
a city
m M
AA Eg
Time min
Total of Tempe and Salt Solution
75ºC 85ºC
95ºC
18
4.2.2 Total Phenolic Content
The total phenolic contents TPC were measured using the Folin- Ciocalteu assay, which was based on the transfer of electrons from phenolic
compounds to the Folin-Ciocalteu reagent in alkaline medium forming blue complexes that can be detected spectrophotometrically at 750
–765 nm Singleton et al. 1999, Cai et al. 2004. As can be seen from Table 3, the fresh tempe
contained phenolic compounds of 1.45 mg of GAEg. When it was subjected to the thermal processing, the TPC changed with the same trend as antioxidant
capacity Figure 8.
Figure 8 Effects of heating on total phenolic content of tempe at 75, 85, and 95
o
C. The increase of TPC occured in salt solution, whereas TPC of tempe
decreased during heating period of 120 min indicating that heat treatments caused water-soluble phenolic compounds leaching into heating medium. Totally heating
0,00 1,00
2,00 3,00
4,00
30 60
90 120
To ta
l p
h en
o li
c co
n te
n t
m g
of G
AEg
Time min
Tempe
75ºC 85ºC
95ºC 0,00
1,00 2,00
3,00 4,00
30 60
90 120
To ta
l p
h en
o li
c co
n te
n t
m g
o f
G AEg
Time min
Salt Solution
75ºC 85ºC
95ºC
0,00 1,00
2,00 3,00
4,00
30 60
90 120
To ta
l p
h en
o li
c co
n te
n t
m g
of G
AEg
Time min
Total of Tempe and Salt Solution
75ºC 85ºC
95ºC
19 of samples increased the total amount of TPC in tempe and salt solution. Heating
of tempe might cause the degradation of polyphenols and release of bound phenolic compositions from the vacuoles Brecht et al. 2008. According to
correlation analysis see Table 4, there were significant correlations between TPC and DPPH scavenging capacity p 0.05 at 75, 85, and 95
o
C in all components of samples. It can be assumed that phenolic compounds strongly influenced the
antioxidant capacity of tempe. The changes of phenolic content in tempe was affected by composition of
phenolic acids. Raw and boiled yellow soybean contained free phenolic acids both benzoic type, such as gallic acid, 2,3,4-trihydroxybenzoic acid, vanillic acid and
protocatechualdehyde, and cinnamic type, such as chlorogenic, sinapic, and trans- cinnamic acid. Moreover, conjugated phenolic acids were also detected in both
raw and boiled yellow soybean, such as benzoic type gallic, protocatechuic, 2,3,4-rihydroxybenzoic, p-hydroxybenzoic, gentistic, syringic, vanillic acid,
protocatechualdehyde and vanillin and cinnamic type caffeic, p-coumaric, m- coumaric, o-coumaric, sinapic and trans-cinnamic acid Xu and Chang 2008.
Thermal processing caused complex variations in phenolic acid profiles of soy products. For instance, boiling soymilk caused significant increases in free
gallic, protocatechuic, 2,3,4-trihydroxybenzoic, sinapic acid, and subtotal benzoic acids Xu and Chang 2009, whereas boiling treatment of yellow soybean
significantly increased 2,3,4-trihydroxybenzoic acid Xu and Chang 2008. In addition, pressure steaming of yellow soybeans caused the increase of benzoic
acid about 23 and also the TPC value about 35. The elevated total phenolic values were correlated to the release of phenolic substances with reactivity toward
Folin-Ciocalteu reagent from polymerized structural substances in cell walls upon thermal processing Xu and Chang 2008.
Table 4 Correlations between antioxidant capacity and total phenolic flavonoid content.
Correlation Coefficient
a
r TPC
TFC 75
o
C 85
o
C 95
o
C 75
o
C 85
o
C 95
o
C DPPH
scavenging capacity
Tempe 0.77 0.89 0.68 0.09 0.83 0.51
Salt solution 0.81 0.69 0.89 0.16
0.32 0.04
Total of tempe and salt solution
0.81 0.49 0.79 0.10 0.21
0.05
a
correlation is significant at the 0.05 level.
4.2.3 Total Flavonoid Content
The total flavonoid contents TFC in tempe was estimated by colorimetric assay involving AlIII-flavonoid complexes formed in solution Deng and Van
Berkel 1998. The results of spectrophotometric analysis showed that before heating the flavonoid compounds of tempe was 0.77 mg of CAEg see Table 3.
According to Figure 9, the TFC was relatively constant during thermal treatments at three different temperatures 75, 85, and 95
o
C. Similar heat effects were found
20 in heating of tomatoes at 88
o
C for 2, 15, and 30 min, which resulted no significant changes in the total flavonoid content Dewanto et al. 2002. The results of
correlation analysis see Table 4 indicated that no significant correlations existed between total flavonoid content and DPPH scavenging capacity p 0.05 except
tempe at 85 and 95
o
C.
Figure 9 Effects of heating on total flavonoid content of tempe at 75, 85 and 95
o
C. In the other hand, Xu and Chang 2009 have studied that traditional stove
cooking increased by 20-23 TFC, steam injection cooking increased by 28-65 TFC, direct Ultra High Temperature UHT processing increased by 48-90 TFC,
and indirect UHT processing increased by 74-113 TFC. The effects of heating at different temperature on changes of TFC in this research can not be observed
distinctly. The spectrophotometric method used were less sensitive to analyze the changes of TFC during thermal treatments. The flavonoid compounds were poorly
occuring in yellow soybean Xu and Chang 2007, thus the more sensitive
0,00 0,30
0,60 0,90
1,20 1,50
30 60
90 120
To ta
l fla
v o
n o
id c
o n
te n
t
m g
o f
C A
Eg
Time min
Tempe
75ºC 85ºC
95ºC 0,00
0,30 0,60
0,90 1,20
1,50
30 60
90 120
To ta
l fla
v o
n o
id c
o n
te n
t
m g
o f
C A
Eg
Time min
Salt Solution
75ºC 85ºC
95ºC
0,00 0,30
0,60 0,90
1,20 1,50
30 60
90 120
To ta
l fla
v o
n o
id c
o n
te n
t
m g
of C
A Eg
Time min
Total of Tempe and Salt Solution
75ºC 85ºC
95ºC
21 methods were required to study the trend of changes in total flavonoid
components, such as High Performance Liquid Chromatoraphy HPLC. The predominant flavonoid compounds in soybean are isoflavones which
its retention and distribution were significantly affected by thermal processing Xu and Chang 2008, Xu and Chang 2009. Although the TFC in this study was
relatively constant, the antioxidant capacity from 80 acetone extract elevated during heating at 75, 85, and 95
o
C see Figure 7. These findings indicated that thermal treatments transformed some compounds which had lower antioxidant
status to higher antioxidant power Xu and Chang 2009. The aglycone forms of isoflavones had stronger antioxidant capacity than the glucosides Hayes et al.
1977, Pratt and Stafforini 1979.
75
o
C 85
o
C
95
o
C Figure 10 Force versus time curves of texture profile analysis during thermal
treatments of tempe.
22
Figure 11 Effects of
heating on
hardness, springiness,
stickiness, cohesiveness, and chewiness of tempe at 75, 85, and 95
o
C.
0,00 0,20
0,40 0,60
0,80 1,00
1,20
10 20
30
H a
rd n
ess k
g
Time min
Hardness
75ºC 85ºC
95ºC 0,00
0,20 0,40
0,60 0,80
1,00 1,20
10 20
30
S p
rin g
in ess
Time min
Springiness
75ºC 85ºC
95ºC
0,00 0,20
0,40 0,60
0,80 1,00
1,20
10 20
30
S tick
in ess
Time min
Stickiness
75ºC 85ºC
95ºC 0,00
0,20 0,40
0,60 0,80
1,00 1,20
10 20
30
Co h
esi v
en ess
Time min
Cohesiveness
75ºC 85ºC
95ºC
0,00 0,20
0,40 0,60
0,80 1,00
1,20
10 20
30
Ch ew
in ess
Time min
Chewiness
75ºC 85ºC
95ºC
23
4.3 Effects of Heating on Physical Quality
4.3.1 Textural Profiles
Texture profile analysis TPA basically simulates the mastication process of humans to give force versus time curves as a function of deformation. Before
heating the fresh tempe had textural characteristics as followed: 1.19 kg of hardness, 0.38 of springiness, 0.21 of stickiness, 0.22 of cohesiveness, and 0.14 of
chewiness. Thermal processing effectively impacted on hardness, whereas other parameters, such as springiness, stickiness, cohesiveness, and chewiness, were
remainly constant when subjected to heating for 30 min Figure 11.
The main texture attribute of vegetables is hardness or firmness Bourne 1989 because it has the best correlation to the consumer acceptance Bourne
1982. According to force-time curves see Figure 10, hardness is the maximum force needed to compress the sample. Most published studies have described
thermal degradation of texture based on hardness characteristic and it is possible to model changes based on other properties, but their relation to consumer
perception has not been well established Rizvi and Tong 1997.
The firmness of various bean was strongly correlated with soluble pectin content increasing due to thermal treatment Huang and Bourne 1983.
Intercellular adhesive material, such as pectin, held the firm texture of cell wall structure. When broken by heat, the pectin was depolymerized, so the resistance
of plant tissue to fracturability loss decreased during heating Loh and Breene 1982. In addition, thermal treatments resulted in plasmolysis which reduces the
turgor pressure of cell wall and caused softening texture Rao and Lund 1986.
The presence of salt NaCl in the medium accelerated the solubility of pectin Van Buren 1986. Hence, the more salt dissolved in solution, the texture of tempe
became softer.
4.3.2 Visual Appearance
Appearance of the food product is the first thing influencing on buying ability of consumers. This is characterized by the color which Hunter L a b model
is often used to analyze the color changes. Another color system recommended by CIE is the L C h system Wrolstad and Smith 2010. Figure 12 shows typical
results on the changes of color parameters of tempe surface for 12 min at different temperatures. Visual inspection could not differ color changes of samples, but the
instrumental analysis using Minolta Chromameter was able to detect the color differences from the surface of samples. The color parameters of fresh tempe were
L = 64.00 lightness, a = -0.30 greenness, b = 3.69 yellowness, c = 3.70 chroma, and H = -88.93 hue see Table 3. During thermal processing, the
lightness, yellowness, chroma, and hue value significantly increased, but the greenness tended to decline slightly.
24
Figure 12 Effects of heating on lightness, greenness, yellowness, chroma, and hue of tempe at 75, 85, and 95
o
C.
64,00 64,50
65,00 65,50
66,00
2 4
6 8
10 12
Lig h
tn ess
L
Time min
Lightness
75ºC 85ºC
95ºC -2,00
-1,50 -1,00
-0,50 0,00
2 4
6 8
10 12
G re
en n
ess a
Time min
Greenness
75ºC 85ºC
95ºC
3,00 3,50
4,00 4,50
5,00
2 4
6 8
10 12
Ye ll
o w
n ess
b
Time min
75ºC 85ºC
95ºC 3,00
3,50 4,00
4,50 5,00
2 4
6 8
10 12
Ch ro
m a
C
Time min
75ºC 85ºC
95ºC
-83,00 -82,50
-82,00 -81,50
-81,00
2 4
6 8
10 12
H u
e h
Time min
75ºC 85ºC
95ºC -83,00
-82,50 -82,00
-81,50 -81,00
2 4
6 8
10 12
H u
e h
Time min
75ºC 85ºC
95ºC
25 According to Clydesdale and Ahmed 1978, object-light interactions may
affect on color measurement of samples, such as reflection from the surface, refraction into the object, transmission through the object, diffusion, and
absorption within the object. Heating tempe in salt solution caused the increase of water content entering into the tissue. When the source light from chromameter
came on the tempe surface, it would be resulted increasing intensity of object-light interactions. In this way, increasing water content of tempe produced the more
reflected light from the tempe surface. This might increase the lightness of tempe and change the other color propeties.
The change of chroma and hue parameters corresponded to the intensity of yellowness and greenness. The elevation of hue angle was influenced by the
increase of yellowness and the decrease of greenness intensity. The chroma had almost similar value to yellowness. Hence, the reduction of greenness value did
not significantly affected on the chroma of tempe.
A food system which contain a carbonyl group of reducing sugar and an amine group of free amino acids subjected to high temperature treatment should
experience the Maillard reaction involving the formation of brown pigmen Kim and Lee 2009. It is well known that tempe contains high protein 23-55 and
also some sugars Kwon et al. 2010. When tempe was heated for certain time, the carbonyl group and amine group might interact to form brown color of Maillard
reaction. But, the presence of salt in heating medium could decrease the rate of Maillard Reaction due to the decrease of water activity value BeMiller and Huber
2008. Therefore, it can be assumed that the use of 2 salt solution as heating medium might be effectively retain the visual appearance of tempe.
4.4 Kinetic Modeling of Quality Changes
Kinetic modeling is one of the quantitative modeling used as indicators of food quality degradation. A systematic way is done to stimulate an appropriate
design process, thus the quality retention of product can be managed well Van Boekel 2008. According to Hindra and Baik 2006, the rate of quality change
strongly relates with to two main factors, product composition moisture content, water activity, pH, etc. and environmental factors time, temperature, etc..
Furthermore, kinetic order reaction is determined by the characteristics of chemical reaction in the product. Most heat induced reactions are assumed to obey
first order kinetic which the reaction rate is proportional to the reactant concentration or quality properties Holdsworth and Simpson 2007.
Determination of quality indicators induced by heating was based on a logaritmic relationship describing the quality attributes as a function of variable
process time and temperature obeying first order kinetic reaction. However, in this study not all tested properties could be modeled well as thermal kinetic
parameters because some of them were not affected significantly by process conditions, such as the total flavonoid content, hue, springiness, stickiness,
cohesiveness, and chewiness. The heat sensitive quality parameters of tempe, such as antioxidant capacity, TPC, hardness, lightness, yellowness, greenness, and
chroma, could be modeled well as first-order reaction with different tendency.
26
Figure 13 Kinetic modeling of DPPH scavenging capacity of tempe during heating at 75, 85, and 95
o
C. The effects of heating at three different temperatures 75, 85, and 95
o
C on radical DPPH scavenging capacity of tempe are shown in Figure 13. The results
of spectrophotometric analysis indicated an increase in antioxidant capacity of total of tempe-salt solution and only salt solution due to thermal treatments. In
contrast, antioxidant capacity of tempe decreased for 120 min during heating period, but the rate of decreasing antioxidant capacity in tempe increased with
increase of temperature k
75
=0.0050, k
85
=0.0051, and k
95
=0.0052 min
-1
. On the other hand, the rate of increasing antioxidant capacity in salt solution k
75
=0.0145, k
85
=0.0150, and k
95
=0.0174 min
-1
was greater than in total of tempe-salt solution k
75
=0.0025, k
85
=0.0026, and k
95
=0.0033 min
-1
. Totally the thermal treatments of tempe at 75 and 85
o
C gave almost same effects on total of tempe-salt solution for 120 min. However, heating at both of temperature was significantly different as
-0,8 -0,4
0,0 0,4
0,8 1,2
1,6 2,0
30 60
90 120
ln CtCo
Time min
Tempe
75ºC: y = -0.0050x, r² = 0.791 85ºC: y = -0.0051x, r² = 0.895
95ºC: y = -0.0052x, r² = 0.828 -0,8
-0,4 0,0
0,4 0,8
1,2 1,6
2,0
30 60
90 120
ln C
t C
o
Time min
Salt Solution
75ºC: y = 0.0145x, r² = 0.951 85ºC: y = 0.0150x, r² = 0.939
95ºC: y = 0.0174x, r² = 0.885
-0,8 -0,4
0,0 0,4
0,8 1,2
1,6 2,0
30 60
90 120
ln C
t C
o
Time min
Total of Tempe and Salt Solution
75ºC: y = 0.0025x, r² = 0.887 85ºC: y = 0.0026x, r² = 0.849
95ºC: y = 0.0033x, r² = 0.880
27 compared to at 95
o
C. It can be assumed that the rate constant of antioxidant capacity significantly changed at temperature up to 85
o
C for 120 min.
Figure 14 Kinetic modeling of total phenolic content of tempe during heating at 75, 85, and 95
o
C. The changes of total phenolic contents during heating expressed as mg of
galic acid equivalentg of sample are shown in Figure 14. When samples were subjected to the thermal processing, the TPC changed with the same trend as
antioxidant capacity showing the decrease in tempe and the increase in salt solution and total of tempe-salt solution. The rate of decreasing TPC in tempe
increased with increase of temperature k
75
=0.0034, k
85
=0.0036, and k
95
=0.0041 min
-1
. Moreover, the TPC of salt solution elevated more quickly k
75
=0.0090,
-0,5 0,0
0,5 1,0
1,5
30 60
90 120
ln CtCo
Time min
Tempe
75ºC: y = -0.0034x, r² = 0.809 85ºC: y = -0.0036x, r² = 0.954
95ºC: y = -0.0041x, r² = 0.888 -0,5
0,0 0,5
1,0 1,5
30 60
90 120
ln CtCo
Time min
Salt Solution
75ºC: y = 0.0090x, r² = 0.908 85ºC: y = 0.0111x, r² = 0.878
95ºC: y = 0.0134x, r² = 0.805
-0,5 0,0
0,5 1,0
1,5
30 60
90 120
ln C
t C
o
Time min
Total of Tempe and Salt Solution
75ºC: y = 0.0029x, r² = 0.778 85ºC: y = 0.0043x, r² = 0.953
95ºC: y = 0.0051x, r² = 0.910
28 k
85
=0.0111, and k
95
=0.0134 min
-1
than in total of tempe-salt solution k
75
=0.0029, k
85
=0.0043, and k
95
=0.0051 min
-1
.
Figure 15 Kinetic modeling of hardness of during heating at 75, 85, and 95
o
C. Figure 15 presents hardness parameter kg of the samples at three
different temperatures. Generally thermal softening in fruits and vegetables was expressed as the first order rate with the firmness as the primary texture attribute
Bourne 1987. The force required to compress tempe decreased during 30 min of thermal treatments. As temperature evelated, the rate of softening tempe increased
k
75
=0.0075, k
85
=0.0126, and k
95
=0.0165 min
-1
which at 95
o
C textural degradation occured most rapidly. Thermal process affected on turgor cell and
changes in wall-pectin composition leading to a decrease in firmness Revilla and Vivar-Quintana 2008, Van Buren 1986.
Typical results on the changes of color parameters of tempe surface for 12 min at different temperatures are shown in Figure 16. The lightness L,
yellowness b and chroma C value increased, but the greenness a tended to decline during thermal processing. It can be seen from the graphs that the rate of
changes in color attribute at 95
o
C occured most rapidly, followed by heating at 85
o
C and lastly at 75
o
C. The increase rate of yellowness k
75
=0.0028, k
85
=0.0076, and k
95
=0.0132 min
-1
and chroma k
75
=0.0033, k
85
=0.0078, and k
95
=0.0132 min
- 1
occured more rapidly as compared to lightness k
75
=0.0005, k
85
=0.0010, and k
95
=0.0014 min
-1
for 12 min of heating. On the other hand, the rate of decreasing in greenness was the greatest k
75
=0.0070, k
85
=0.0126, and k
95
=0.0207 min
-1
among other color parameters. The chroma influenced by yellowness and greenness had almost similar value to yellowness intensity. Hence, the reduction
of greenness value did not significantly affected on the chroma of tempe.
-0,60 -0,40
-0,20 0,00
0,20
5 10
15 20
25 30
ln H
tHo
Time min
Hardness
75ºC: y = -0.0075x, r² = 0.938 85ºC: y = -0.0131x, r² = 0.870
95ºC: y = -0.0172x, r² = 0.921
29
Figure 16 Kinetic modeling of lightness, greenness, yellowness, and chroma during heating at 75, 85, and 95
o
C.
4.5 Activation Energy of Quality Changes
The Arrhenius equation described the effects of typical temperature ranges on tempe attribute changes during thermal process. This model is to regress the
natural logarithm of the reaction rate constant, Ink, versus the reciprocal of the absolute temperature, 1T, to obtain the estimates of Ink
, the intercept and EaR, the slope index of the regression line Van Loey et al. 1995. The Arrhenius plot
of antioxidant activity and physical changes of tempe is given in Figure 17. It can be seen from the curves that the slope for degradation of physical properties was
-0,30 -0,15
0,00 0,15
2 4
6 8
10 12
ln LtLo
Time min
Lightness
75ºC: y = 0.0005x, r² = 0.947 85ºC: y = 0.0010x, r² = 0.898
95ºC: y = 0.0014x, r² = 0.942 -0,30
-0,15 0,00
0,15
2 4
6 8
10 12
ln a
ta o
Time min
Greenness
75ºC: y = -0.0070x, r² = 0.962 85ºC: y = -0.0126x, r² = 0.974
95ºC: y = -0.0207x, r² = 0.997
-0,30 -0,15
0,00 0,15
2 4
6 8
10 12
ln b
tb o
Time min
Yellowness
75ºC: y = 0.0028x, r² = 0.952 85ºC: y = 0.0076x, r² = 0.970
95ºC: y = 0.0132x, r² = 0.944 -0,30
-0,15 0,00
0,15
2 4
6 8
10 12
ln C
tCo
Time min
Chroma
75ºC: y = 0.0033x, r² = 0.938 85ºC: y = 0.0078x, r² = 0.897
95ºC: y = 0.0132x, r² = 0.939
30 sharper than antioxidant capacity indicating that the rate of physical change was
more heat sensitive than other parameter.
Key: AC= antioxidant capacity, TPC= total phenolic content, h= hardness, L= lightness, G= greenness, Y= yellowness, C= chroma, T= tempe, S= salt solution, TS= total of tempe and salt
solution.
Figure 17 Arrhenius plot for antioxidant properties and physical changes of tempe at 75, 85, and 95
o
C. The activation energy E
a
Table 5, which represents the least amount of energy needed for a chemical reaction to take place, was calculated by the slope of
curves E
a
R. The activation energy also indicated the parameter sensitivity to temperature changes. Determination of activation energy from physical attributes
showed that activation energies for color changes were greater than textural changes meaning that color properties were more heat sensitive than textural
attributes. The activation energy for antioxidant capacity was smaller than total phenolic content meaning that TPC was more heat sensitive than antioxidant
-8 -6
-4 -2
0,0027 0,0028
0,0029
ln k
1 m
in
1T 1K
Antioxidant Properties
AC T AC S
AC TS TPC T
TPC S TPC TS
-8 -6
-4 -2
0,0027 0,0028
0,0029
ln k
1 m
in
1T 1K
Physical Quality
H T L T
G T Y T
C T
31 capacity of tempe. A positive value of E
a
means that the reaction rate increases with increasing temperature. The information from Arrhenius parameters can be
used to optimize thermal process and maximize quality retention of tempe by choosing an appropriate time-temperature combination.
Table 5 Activation energy for antioxidant properties and physical quality of tempe during thermal treatments.
Parameters Component
Equations r²
Ea kJmol
Antioxidant capacity
Tempe y = -251.1x
– 4.5769 0.999
2.09 Salt solution y = -1160.3x
– 0.9188 0.873 9.65
Total y = -1765.4x
– 0.952 0.842
14.68 Total phenolic
content Tempe
y = -1194.1x – 2.2653 0.945
9.93 Salt solution y = -2549.3x + 2.6167
0.999 21.19
Total y = -3627.2x + 4.6135
0.957 30.16
Hardness Tempe
y = -5330.3x + 10.467 0.968
44.32 Lightness
Tempe y = -6612.4x + 11.453
0.968 54.98
Greenness Tempe
y = -21823x + 58.122 0.868
181.44 Yellowness
Tempe y = -9952.8x + 22.787
0.978 82.75
Chroma Tempe
y = -8894.3x + 19.892 0.985
73.95
4.6 Application of Kinetic Data
Design of optimal thermal processing relies on kinetic of bacterial inactivation and quality changes Van Loey et al. 1995.
The destruction of microorganisms and quality factors does not proceed at the same rate Stumbo 1973,
Holdsworth 1985.
Commonly, every 10
o
C rise in temperature the rate of chemical reaction elevates two-fold, while the rate of microbial destruction rises ten-fold or
in other words quality deterioration is less heat sensitive than microbial destruction Holdsworth 1985. Because of the differences in thermal behaviour
between safety and quality factors, optimization is required to ensure the product safety and maximize retention of quality attributes.
A conventional thermal process blanching, pasteurization, and sterilisation often leads to undesirable changes in food quality, such as color,
texture, flavor, nutrition, and functionality Ndiaye et al. 2009. An accurate kinetic data of microbial inactivation and quality loss can be applied to estimate
the effects of time-temperature process on product quality desired. Heating
at higher temperatures is relatively lower destruction of quality factors. In addition,
when the heat transfer rate is enhanced then the process will be shorter resulting in lesser destruction in quality factors and this forms HTST High Temperature Short
Time concept Rattan 2012.
Figure 18 illustrates the application of kinetic parameters of tempe to determine the appropriate time-temperature combination during thermal process.
Tempe belongs to low acid food products, thus the thermal process considers both public health Clostridium botulinum and spoilage thermophilic organisms
